This application claims the benefit of and priority from Japanese Applications No. 2001-360375 filed Nov. 27, 2001 and No. 2001-360379 filed Nov. 27, 2001, the content of which are incorporated herein by reference.
1. Field of the Invention
The present invention pertains to a brake hose having two reinforcing yarn layers including a lower yarn layer and an upper yarn layer in a rubber base.
2. Description of the Related Art
A brake hose known in the conventional art is shown in FIG. 16 (JP 06-201076A). FIG. 16 is a cross-section of the main components of a conventional brake hose 200. Because the brake hose 200 must have high resistance against brake fluid pressure, it is formed from several layers of rubber and fiber yarn. The brake hose 200 comprises an inner tube rubber layer 202, a lower yarn layer 204, an intermediate rubber layer 206, an outer yarn layer 208, and a cover rubber layer 210.
The brake hose 200 is required to meet a higher pressure resistance standard than a coolant system hose or a fuel system hose. As fluid temperatures and pressure levels of automobile system have increased in recent years, the demand for higher pressure resistance has increased as well.
The pressure from the pressure fluid flowing in the flow path 201 inside the brake hose 200 is transmitted from the inner circumference area of the brake hose 200 to the outer circumference area thereof. In other words, the pressure is transmitted to the inner tube rubber layer 202, the lower yarn layer 204, the intermediate rubber layer 206, the upper yarn layer 208 and the cover rubber layer 210, causing each layer to expand. Each layer has a binding force that operates against the pressure exerted by the pressure fluid and inhibits expansion of such layer. The inner tube rubber layer 202, the intermediate rubber layer 206 and the cover rubber layer 210 are highly elastic, and are responsible for no more than 10% of the total binding force, while the majority of the binding force is possessed by the lower yarn layer 204 and the upper yarn layer 208. Consequently, increasing the binding force of the lower yarn layer 204 and the upper yarn layer 208 increases the durability and expansion resistance (i.e., resistance to cubical expansion) provided by the brake hose 200. As a result, increasing both of these characteristics by changing the type of yarn material used and the braiding method of the yarn layers has been examined.
An object of the present invention is to provide a brake hose that offers increased durability and expansion resistance.
In accordance with one embodiment of the present invention, a brake hose includes two reinforcing layers in a rubber base. The brake hose comprises an inner tube rubber layer having a flow path for flowing fluid, a lower yarn layer formed by braiding first yarns around the inner tube rubber layer and an upper yarn layer formed by braiding second yarns around the lower yarn layer and a cover rubber layer covering the upper yarn layer. A lower yarn layer duty LD given by the equation, LD(%)=(LRP/PRP)xc3x97100, has a value of 50-65%, LRP denotes an inner pressure at which a brake hose without the upper yarn layer and the cover would burst, and PRP denotes an inner pressure at which the brake hose would burst.
In the brake hose pertaining to the present invention, the pressure exerted by the pressure fluid flowing in the flow path is transmitted from the inner circumference area of the brake hose to the outer circumference area thereof, i.e., from the interior of the rubber base to the lower yarn layer and the upper yarn layer, causing each such layer to expand. A binding force that restricts the expansion of the brake hose in resistance to the pressure from the pressure fluid is generated. The rubber base is responsible for no more than 10% of the total binding force due to its high elasticity, while the majority of the binding force is exerted by the lower yarn layer and the upper yarn layer.
Because the fluid pressure transmitted in this fashion travels from the inner circumference area to the outer circumference area of the brake hose in a radial fashion, the fluid pressure diminishes per unit area as it travels to the outer circumference area, and the lower yarn layer in the inner circumference area of the brake hose receives a larger amount of expansion force than the upper yarn layer. As a result, where the lower yarn layer and the upper yarn layer are formed from yarn made of the same material, the yarn of the lower yarn layer receives a greater tensile force than the yarn of the upper yarn layer. This means that even where the first yarns bursts after receiving a large amount of tensile force, there is still some degree of margin or leeway before the second yarns bursts. In view of this fact, the percentage burden assumed by the lower yarn layer is set at 50-65% of the total burden. In other words, the percentage burden assumed by the second yarns is set to a value larger than in a conventional brake hose, while the burden assumed by the first yarns is reduced. Consequently, the burden on each individual strand of yarn becomes smaller, and the ultimate rupturing pressure that may be applied to the brake hose can be increased.
The percentage burden assumed by the lower yarn layer is set to 50-65% because the first yarns and second yarns must satisfy prescribed levels of tensile strength and elongation. Therefore, a material such as vinylon, polyethylene terephthalate, polyethylene naphthalate or rayon is used, for example, because it would be difficult as a practical matter to set the percentage burden to be assumed by the lower yarn layer at less than 50% using these yarns, while if the lower yarn layer percentage burden were to exceed 65%, the higher rupturing pressure that comprises one characteristic of the present invention could not be obtained.
It is preferred that the second yarns of the upper yarn layer has a lower elongation than the first yarns of the lower yarn layer. Because the upper layer yarn is less subject to elongation when subjected to tensile force, it can handle a large amount of force up to the point at which the lower yarn layer expands and bursts.
For example, yarn having a tensile strength of 8.5 g per decitex and a elongation of 3.0xc2x11% at a tensile load of 2.7 g can be used for the second yarns, and yarn having a tensile strength of 6.5 g per decitex and a elongation of 3.5xc2x11% at a tensile load of 2.7 g can be used for the first yarns. A decitex is a unit of measurement that expresses the weight(2) of a fiber relative to its length, and is equal to one gram per 10,000 meters of yarn.
The brake hose according to another aspect of the present invention comprises an inner tube rubber layer that has a flow path in which a pressure fluid flows and is formed from a rubber material, a lower yarn layer formed via braiding of first yarns around this inner tube rubber layer, an upper yarn layer that is formed via braiding of second yarns around this lower yarn layer, and a cover rubber layer that is formed around this upper yarn layer. The lower yarn layer is formed from first yarns strands that have on the surface thereof an adhesive thin film formed via RFL processing and a rubber thin film composed of EPDM that adheres to the adhesive thin film and the inner tube rubber layer, such layers formed in a sequential order. EPDM refers to ethylene-a-olefin-unconjugated diene copolymer (propylene as a-olefin).
The above-mentioned first yarns comprises a filament bundle composed of bundled filament threads, on each of which is formed an undercoat layer using an epoxy primer process. The above-mentioned adhesive thin film and rubber thin film are sequentially applied to the outer surface of each filament bundle.
The above-mentioned first yarns comprises a filament bundle composed of bundled filament threads. An undercoat is formed on the outer surface of each filament bundle using an epoxy primer process, and an adhesive thin film and rubber thin film are then applied over the undercoat.
In the brake hose pertaining to the present invention, the lower yarn layer and the upper yarn layer formed around the inner tube rubber layer form two reinforcing yarn layers inside the rubber base, and give the brake hose sufficient strength to withstand the high pressure of the pressure fluid flowing within the flow path. Furthermore, the first yarns constituting the lower yarn layer includes an adhesive thin film formed via RFL processing and a rubber thin film. The rubber thin film adheres to the inner tube rubber layer and prevents yarn displacement, increases the solidity of the lower yarn layer by causing the strands of the first yarns to adhere to each other at areas where they overlap, which prevents the inner tube rubber layer from expanding due to internal pressure, thereby limiting the amount of cubical expansion of the brake hose and improving the feel of the brake. The adhesive thin film formed via RFL processing is formed in order to cause the first yarns to adhere to the rubber thin film formed from EPDM. In RFL processing, an adhesive thin film that operates as an adhesive and is formed mainly from resorcinol-formaldehyde-latex resin and rubber latex is applied to the surface of each yarn strand.
In the brake hose according to another aspect of the present invention, because an intermediate rubber layer is not formed around the lower yarn layer, the process of forming the intermediate rubber layer can be omitted. As a result, when a manufacturing run of brake hoses is produced, the significant amount of floor space required for forming the intermediate rubber layer is no longer required.
In a preferred embodiment of the first yarns, a filament bundle is formed by bundling together several hundred filament threads, over each of which is formed an undercoat layer using an epoxy primer process, and then forming over the filament bundle a layer formed via RFL processing and an EPDM layer. The lower yarn layer is then formed by braiding the first yarns around the inner tube rubber layer. In this case, because the filament threads adhere strongly to each other due to the undercoat layer, the penetration of air or brake fluid between the filament threads can be prevented more effectively.
In another preferred embodiment of the first yarns, a filament bundle is formed by bundling together filament threads, an undercoat is formed on the outer surface of the filament bundle using an epoxy primer process, and an adhesive thin film and a rubber thin film are sequentially formed over the undercoat layer. In this case, because the epoxy primer process is not performed for each individual filament thread, and is instead carried out for the filament bundle as a whole, manufacturing efficiency can be improved.